Apparatus for separating vapor from a viscous liquid

ABSTRACT

An apparatus is provided for separating vapor from a viscous liquid flowing through a horizontal conduit to the top of an enclosed upright cylindrical vessel and distributing the liquid uniformly to a melt pool centrally rotating about the axis of the vessel. The apparatus comprises a tee-shaped conduit connected to the horizontal conduit so that the through passage of the tee is vertically aligned and enters the vessel. The tee is capped at its upper end. A plate is diametrically positioned in the through passage with one end spaced from the capped end of the tee. The plate extends downwardly beyond the horizontal conduit into the lower end of the tee. A nozzle having a plurality of orifices there-through is connected to the lower end of the tee. The nozzle is in the shape of a sector of a circle with its tip located on the axis of the vessel and has a radius approximately equal to that of the melt pool.

nited States Patent [191 lwasyk et al.

[45] Febg M W. Rodeffer, New Castle, both of Del.

[73] Assignee: E. I. du Pont de Nemours and Company, Wilmington, Del.

22 Filed: on. 19,1972

21 Appl. No.: 299,094

[52] US. Cl. 55/201 [51] Int. Cl B0111 57/00 [58] Field of Search...23/283, 285; 55/41, 52, 192,

[56] References Cited 9/1969 Siclari et a1 159/48 10/1969 Halder et a1.23/285 Primary Examiner-Samih H. Zaharna Assistant ExaminerRichard W.Burks An apparatus is provided for separating vapor from a viscousliquid flowing through a horizontal conduit to the top of an enclosedupright cylindrical vessel and distributing the liquid uniformly to amelt pool centrally rotating about the axis of the vessel. The apparatuscomprises a tee-shaped conduit connected to the horizontal conduit sothat the through passage of the tee is vertically aligned and enters thevessel. The tee is capped at its upper end. A plate is diametricallypositioned in the through passage with one end spaced from the cappedend of the tee. The plate extends downwardly beyond the horizontalconduit into the lower end of the tee. A nozzle having a plurality oforifices there-through is connected to the lower end of the tee. Thenozzle is in the shape of a sector of a circle with its tip located onthe axis of the vessel and has a radius approximately equal to that ofthe melt pool.

4 Claims, 7 Drawing Figures PATENIED 5874 3.789584 saw 2 Bf 3PATENTEDFEB 519M SHEU 3 If 3 APPARATUS FOR SEPARATING VAPOR FROM AVISCOUS LIQUID BACKGROUND OF THE INVENTION This invention relates to theproduction of synthetic polymeric material and, more particularly, to anapparatus useful in producing such material.

Condensation polymers such as the polyamides were initially produced bybatch processes in autoclaves, but continuous polymerization processeshave been developed and are generally preferred for present daycommercial operation. A typical continuous polymerization process(abbreviated CP process herein, for convenience) is described by Li inUS. Pat. No. 3,113,843. The apparatus elements shown in FIG. 1 of Liinclude a first reactor 10, in which an aqueous polyamideformingcomposition is partially polymerized at amidation pressure andtemperature; a second reactor 12 wherein polymerization continues atamidation temperature while the pressure is reduced to atmospheric orbelow, while flashing off steam and a steam polymer separator 14 inwhich the steam generated by continuing polycondensation is separatedfrom the polymer. For polymer of especially high molecular weight, theseparator 14 is conventionally followed by a finisher 16.

Although CPs such as the above and others described in the prior art,function very satisfactorily for the commercial nylons of moderate meltviscosity such as are conventional for poly (hexamethyleneadipamide),the increasing need for ever higher mol. wt. polyamides and thedevelopment of polyamides which because of their molecular structurehave very high melt viscosity, require new CP technology adapted tohandle these viscosities which are typically 5 to 50 times that of 66nylon used for textile yarns. For some of these polyamides, it ispossible to simplify equipment somewhat since they do not form gel onheating which is an ever present problem with adipamide polymers.

It is, therefore, an object of the present invention to provide animproved terminal unit for the flash tube 12, whereby the high velocitysteam is disengaged from high viscosity polyamide while the lattercontinues to polymerize. The invention further provides for separationof steam and polymer and for uniformly distributed delivery of polymerto a slowly rotating pool of molten polyamide. The apparatus of thepresent invention also has sufficient flexibility so that it is operableat throughput rates over at least a 5 fold range while maintainingconstant product characteristics.

SUMMARY OF THE INVENTION An apparatus is provided for separating vaporfrom a viscous liquid flowing through a horizontal conduit to the top ofan enclosed upright cylindrical vessel and distributing the liquiduniformly to a melt pool centrally rotating about the axis of thevessel. The apparatus comprises a tee-shaped conduit connected to thehorizontal conduit so that the through passage of the tee is verticallyaligned and enters the vessel. The tee is capped at its upper end. Aplate is diametrically positioned in the through passage with one endspaced from the capped end of the tee. The plate extends downwardlybeyond the horizontal conduit into the lower end of the tee. A nozzlehaving a plurality of orifices therethrough is connected to the lowerend of the tee.

The nozzle is in the shape of a sector of a circle with its tip locatedon the axis of the vessel and has a radius approximately equal to thatof the melt pool. I

BRIEF DESCRITPION OF THE DRAWINGS FIG. 1 is a schematic illustration ofthe Cl disclosed by Li, modified with the terminal unit for the flashtube which discharges through baffled tee-shaped conduit into a steampolymer separator.

FIG. 2 is a schematic illustration of a steam polymer separator with themelt distribution nozzle in place.

FIGs. 3 and 4- are detailed plan and elevation views of the meltdistribution nozzle.

FIG. 5 shows a prior art steam nozzle which is preferred for use withthe instant invention.

FIGS. 6 and 7 show in elevation and plan another embodiment of the meltdistribution nozzle.

DETAILED DESCRIPTION OF THE INVENTION The polyamide melt and steam feedcomposition may be prepared by employing the apparatus arrangement shownin FIG. ll, wherein polyamide-forming diamine and dicarboxylic acidreactants in aqueous solution are heated under pressure in reactor 10 toform low molecular weight polymer. It may sometimes be desirable to usetwo or more reactors 10, in series, so that the reaction can be carriedout in stages at different temperatures and/or pressures. The reactor orreactors are conventionally heated by a jacket 20 which may containdiphenyl-diphenyl oxide vapor or other conventional heating fluid.

The partially polymerized composition containing solvent water and waterformed by polyamidation is released from reactor l0 through valve 24 viaconduit 22 to flash tube 12. Flash tube 12 may consist of three sections26, 28, 30, of tubing which are series connected and of successivelyincreased diameter. The tubes 26-30 are surrounded by a heating jacket32 to which heating fluid is supplied through pipe 34.

In accord with the invention, the output of reaction products from thetube 30, are passed to a greatly enlarged section of horizontallydisposed pipe 35, hereinafter called a tail pipe, in which the polymerchanges its flow regime from annular to wave, or from annular towave-annular, thus, allowing the steam to disengage itself from thepolymer and occupy the upper portion of tail pipe 35. The steam andpolymer impinge on baffle 37 which is diametrically positioned in tee 38from somewhat below the capped or upper end of the tee to a point in thelower end of the tee. The polymer flows downward in half (39) of conduit36, on its way to the melt pool 40 in steam polymer separator 14. Thesteam passes over the top of baffle 37 and is diverted downward by theclosed end of tee 38 into steam polymer separator 14 via the other halfof conduit 36. Both steam and polymer are delivered to separator 14 byspecially designed nozzles shown in FIG. 2 but not shown in FIG. 1.Steam which is disengaged from the polymer leaves separator 14 throughsteam vent 41 which may be attached to a condenser, vacuum pump, oraspirating jets (not shown), depending on the reaction conditionsdesired in separator 14-.

The polymer discharged collects in melt pool 40 from which it isdischarged at 42 by conventional means (not shown).

It will be apparent that all of vessel 14 and conduits 35, 36 and 38must be provided with suitable heating jackets (not shown).

FIG. 2 shows the separator 14 and associated equipment in somewhatgreater detail. For clarity, conduit 36 has been turned through 90 sothat baffle 37 is in the plane of the figure and tail pipe 35 isperpendicular to the figure. FIG. 2 shows melt distributor nozzle 43 andsteam nozzle 44. Baffle 37 leaves the center line of conduit 36 belowthe bend in 36 and is so constructed as to divert all the steam throughopening 45 in the side of conduit 36, and thence, to steam nozzle 44.The polymer accumulates in a layer in pie-shaped melt distributionnozzle 43, whence, it falls in a plurality of streams into melt pool 40.Conduit 36 is show as having a bend or dog leg this is preferred but isnot essential to uniformize the distribution of melt onto nozzle 43.

FIG. 3 shows a plan view of the melt distribution noz zle 43, while FIG.4 shows the same nozzle in sectioned elevation attached to conduit 36.As is apparent from FIG. 3, the melt outlet nozzle has the configurationof the sector ofa circle. It delivers the polymer to the melt pool in aplurality of streams, via rectangular orifices 46. The transverse rowsof orifices are separated by wedge-shaped bars 47 which help to providea small resistance to flow needed to retain enough polymer above thenozzle so that it is always completely covered with polymer even atlowest throughput. The bars are wedge-shaped (apex upward) so as toavoid forming stagnant polymer areas between the rows of holes.Additional flow resistance is furnished by a series of rods 48 welded tothe bottom of the wedges 47; these rods also serve to prevent thepolymer streams form coalescing below the nozzle.

Desirably, within the geometrical limits imposed by the shape of thenozzle, the hole area (and number of holes, if uniform in size) shouldincrease in proportion to the radial distance from the apex of thenozzle so that the polymer discharged will be evenly distributed overthe rotating melt pool below. It is also essential, as indicatedpreviously, to have enough hole area so that the polymer layer does notbuild up at high throughput rates so that it overflows into the steamside of conduit 36.

FIG. 5 shows a suitable nozzle which may be used as steam nozzle 44. Itis the nozzle shown in FIG. 3 of U.S. Pat. No. 3,134,655 and is notclaimed herein. Its special feature is embodied in the two notches withrooflike diverters 49 which divide any entrained polymer flowing downthe walls of the nozzle so that it is not spattered by escaping steamonto the walls of separator 14.

FIGS. 6 and 7 show in elevation and plan another embodiment of meltdistributor nozzle 43. As seen in FIG. 7, the nozzle has the same sectorshape as in FIG. 3, but employs circular polymer distribution holes 50.These are conveniently drilled in a block of metal 51 which is weldedinto the bottom of conduit 36. The holes are drilled in the bottom oftransverse V-shaped grooves 52, milled in 51 before assembly, to providea streamline entrance to the orificies and avoid stagnant areas.

The steam polymer separator 14 (FIG. 2) into which nozzle 43 dischargesmolten polymer, is a rather tall, cylindrical vessel with its axisvertical. The vessel has a conical bottom 51, which directs the polymermelt to a screw pump 52. Attached to the upper end of the screw of thepump 52 is a conical basket-like arrangement 53 and a cup, open top andbottom which (in combination) serve to provide plug type flow of the onthe axis of separator 14 and its base close to the wall of 14, and sinceit delivers polymer uniformly over a sector of the melt pool immediatelybelow, it necessarily follows that an even layer of molten polymer islaid down on the melt pool as it is rotated by basket 53 and cup 54.

The advantages of the invention ar eobtained by passing a high velocitymixture of steam and polyamide melt from a conventional flash tube ofdiameter d into a conduit oflarger diameter d whereby the flow mode ofthe melt changes from wave-annular to wave or from annular to waveannular while the high velocity steam is disengaged from the polymer. Tochange the flow pattern, the ratio of d. to d must be criticallyselected to avoid unstable or slug flow and to maximize holdup. Theseparated steam and polymer melt impinge on a vertically disposedbaffle, the melt falling downward under the influence of gravity anddischarging from a nozzle of special construction into a slowly rotatingpool of molten polymer. The melt pool is contained in a vessel adaptedto complete the separation of steam and polymer and provide additionalhold-up time for further polymerization under vacuum, if desired. 7 r In I The "HEEgZg'd' st eam, essentially free from entrained polymer,passes over the top of the baffle, then downwards, discharging into thevapor space above said rotating melt pool.

The disengaged steam is vented from the separator vessel into theatmosphere, optionally through a vacuum pump or jet. "TiiifieFHEtriEhiornozzle has an outlet which is shaped like the sector of a circle ofradius approximately equal to that of the melt pool and with the tip ofthe sector approximately on the axis of the separator vessel. Thedistributor nozzle terminates in an apertured grille providing enoughflow resistance so that polymer collects in a layer which is at leastdeep en dii glff covrall the operi ings; the new resistance of thegrille is kept low enough so that even at maximum throughput, the meltdoes not build up and flood over into the steam discharge. The flowresistance is kept small by providing a large number of adequately sizedopenings which are spaced at least about 1/8 inch apart. This spacingprevents the melt streams from C0- alescing, thereby, providing auniform distribution as they fall into the melt pool. The distributionof the melt streams is such that they increase in number in proportionto the radial distance from the sector apex of the nozzle, thereby,distributing the melt uniformly in a radial direction onto the surfaceof the rotating melt pool.

The rotating melt pool, the means by which it is rotated, and the steampolmer separator vessel containing it form no part of the instantinvention; the instant invention is, of course, especially adapted andhas a major utility to supply such a vessel and its melt pool withproperly separated, high viscosity polymer.

It is evident that the diameter d of tail pipe 35 must be carefullyselected if the proper wave-type of fluid flow is to exist in it, forany given conditions of polymer viscosity, polymer flow rate, steam flowrate and flasher tube diameter d For general purposes, the proper pipediameter d for any pipe d can be determined by selecting pipe sizes thatwill put operating conditions in the stratified, wave or wave-annularregion of a Baker plot (see Oil and Gas Journal, Nov. 19, 1958, pp.156-167).

When the gas is steam at 1 atmosphere and 310C., and the polymer isessentially of unit specific gravity, as in the Example, d is selectedsuch that steam flow G, in lbs. per seconds per square foot of pipearea, lies between 0.01 and 10,

The length of the pipe is adjusted to provide the desired hold-up timefor further reaction, if needed.

The following example illustrates the operation of the apparatus of theinvention at a throughput of 70 lbs. polymer per hour, usingcomputations based on experimental data.

EXAMPLE This example shows the use of the apparatus of the inventionwith a polyamide which is the reaction product of bis(4-aminocyclohexyl) methane (70 percent trans-trans stereoisomer) anddodecane dioic acid (identified as PACM-12, for convenience).

Partly polymerized, low molecular weight PACM-12 polymer of about 7500mol. wt. and associated steam are discharged from the outlet of flasher112 (FIG. 1). The flasher tail pipe 35 and conduit 36 are maintained at310C. The weight ratio of polymer to steam is 0.53 to 0.47. Within tube30, which has an internal diameter of 1.05 inches, the flow is of thewave-annular type. At the flash tube exit, the polymer has a meltviscosity of about 180 poise.

The steam polymer mixture is discharged into tail pipe 35 which has aninside diameter of 3.8 inches. This tail pipe is 5 ft. in. long and thetapered transition piece is 1 ft. 4 in. long. The flow becomes wave-typewithin the enlarged tail pipe; the polymer fills about 55 percent of thevolume of the pipe. The holdup time for the polymer in the pipe is about20 min. At the outlet of the pipe at baffle 37, the molecular weight is12,000 and the melt viscosity is 1200 poise.

Steam is separated from the polymer and the polymer is distributeduniformly onto the melt pool as it flows from nozzle 43 which isconstructed as shown in FIGS. 3 and 4. The steam is discharged fromnozzle 44 (as shown in FIG. 5) and leaves separator vessel 14 throughside vent pipe 41.

The apparatus operates smoothly without forming polymer slugs andwithout channeling."

Although the operation of the apparatus of the invention has beenillustrated in terms of PACM-12 polyamide, it is not, of course, limitedto this polymer. lts utility is greatest when processing any polymerhaving a melt viscosity (at processing temperatures) of 1000 to 5000poise or higher, and from which one wishes to separate a volatilereaction product or solvent. The flash tube 35 is especially useful forother than adipamide polymers due to the tendency of the polyadipamidesto form gel when in contact with heated surfaces at low flow rates, in35; even with such polymers, gel deposition can be minimized oreliminated by injecting additional steam into the flash tube at somepoint ahead of the tail pipe.

What is claimed is:

11. An apparatus for separating vapor from a viscous liquid flowingthrough a horizontal conduit to the top of an enclosed uprightcylindrical vessel and distributing said liquid uniformly to a melt poolcentrally rotating about the axis of said vessel, said apparatuscomprising: a tee-shaped conduit connected to said horizontal conduit,the through passage of the tee being vertically aligned and enteringsaid vessel, said tee being capped at its upper end; a platediametrically positioned in said through passage, said plate having oneend spaced from the capped end of the tee, said plate extendingdownwardly beyond said horizontal conduit into the lower end of the tee;and a nozzle having a plurality of orifices therethrough connected tosaid lower end, said nozzle being in the shape of a sector of a circleand having a radius approximately equal to that of the melt pool, saidsector having a tip located on the axis of said vessel.

2. The apparatus of claim 1, the area of said orifices increasing inproportion to the radial distance from the tip of said nozzle.

3. The apparatus as defined in claim 11, said liquid having a viscosityof from 1000 to 5000 poise.

4. An apparatus for separating vapor from a viscous liquid flowingthrough a horizontal conduit to the top of an enclosed uprightcylindrical vessel and distributing said liquid uniformly to a melt poolcentrally rotating about the axis of said vessel, said apparatuscomprising: a tee-shaped conduit connected to said horizontal conduit,the through passage of the tee being vertically aligned and enteringsaid vessel, said tee being capped at its upper end; a platediametrically positioned in said through passage, said plate having oneend spaced from the capped end of the tee, said plate facing andextending downwardly beyond said horizontal conduit into the lower endof the tee dividing said through passage in half, one of the halves ofsaid passage being adjacent said horizontal conduit for transportingsaid viscous liquid, the other half for transporting steam separatedfrom said liquid impinging said plate; and a nozzle having a pluralityof orifices therethrough connected to said one half of said throughpassage at said lower end of the tee, said nozzle being in the shape ofa sector of a circle and having a radius approximately equal to that ofthe melt pool, said sector having a tip located on the axis of saidvessel.

* =l= l l=

1. An apparatus for separating vapor from a viscous liquid flowingthrough a horizontal conduit to the top of an enclosed uprightcylindrical vessel and distributing said liquid uniformly to a melt poolcentrally rotating about the axis of said vessel, said apparatuscomprising: a tee-shaped conduit connected to said horizontal conduit,the through passage of the tee being vertically aligned and enteringsaid vessel, said tee being capped at its upper end; a platediametrically positioned in said through passage, said plate having oneend spaced from the capped end of the tee, said plate extendingdownwardly beyond said horizontal conduit into the lower end of the tee;and a nozzle having a plurality of orifices therethrough connected tosaid lower end, said nozzle being in the shape of a sector of a circleand having a radius approximately equal to that of the melt pool, saidsector having a tip located on the axis of said vessel.
 2. The apparatusof claim 1, the area of said orifices increasing in proportion to theradial distance from the tip of said nozzle.
 3. The apparatus as definedin claim 1, said liquid having a viscosiTy of from 1000 to 5000 poise.4. An apparatus for separating vapor from a viscous liquid flowingthrough a horizontal conduit to the top of an enclosed uprightcylindrical vessel and distributing said liquid uniformly to a melt poolcentrally rotating about the axis of said vessel, said apparatuscomprising: a tee-shaped conduit connected to said horizontal conduit,the through passage of the tee being vertically aligned and enteringsaid vessel, said tee being capped at its upper end; a platediametrically positioned in said through passage, said plate having oneend spaced from the capped end of the tee, said plate facing andextending downwardly beyond said horizontal conduit into the lower endof the tee dividing said through passage in half, one of the halves ofsaid passage being adjacent said horizontal conduit for transportingsaid viscous liquid, the other half for transporting steam separatedfrom said liquid impinging said plate; and a nozzle having a pluralityof orifices therethrough connected to said one half of said throughpassage at said lower end of the tee, said nozzle being in the shape ofa sector of a circle and having a radius approximately equal to that ofthe melt pool, said sector having a tip located on the axis of saidvessel.